1. Field of the Invention
The present invention relates to a spin memory and a spin FET (field effect transistor) that use a magneto-resistance element.
2. Description of the Related Art
In recent years, an attempt has been actively made to apply a magneto-resistance element to an MRAM (Magnetic Random Access Memory).
Lately, a magneto resistance change rate of 230% or more can be obtained and a decrease in magneto resistance change rate when an applied voltage is increased can be restricted, and thus, applicability to the MRAM has been enhanced. In the case where a TMR (Tunneling Magneto Resistance) element is employed as a memory element of MRAM, one ferromagnetic layer sandwiching a tunnel barrier layer is defined as a magnetic pinned layer, and the other ferromagnetic layer is defined as a magnetic free layer. A memory element using these ferromagnetic single tunneling junction or ferromagnetic double tunneling junction has a potential that a write/read time is as fast as 10 nanoseconds or less in nonvolatile property and the write/erase count is 1015 or more.
In the case of a magnetic field write system MRAM, at the time of writing into a magnetic free layer, inversion of magnetization of the magnetic free layer is carried out in only a magnetic field due to a current pulse. Therefore, there occur problems that power consumption is larger, when a large capacity is achieved, the allowable current density of wires is limited, making it impossible to achieve a large capacity, and an area of a drive for supplying a current becomes large.
In order to cope with the problems described above, there has been proposed an MRAM provided with a thin film made of a high permeability magnetic material at the periphery of a write line. In the write line provided with a thin film made of this high permeability magnetic material, a magnetic field is efficiently generated, thus making it possible to reduce a current value required for writing information into a magnetic free layer. However, in this case as well, it has been very difficult to restrict a write current to 1 mA or less.
In order to solve these problems, a writing method using a spin injection magnetization inversion technique is proposed (refer to U.S. Pat. No. 6,256,223, for example). In this spin injection magnetization inversion technique, magnetization of a magnetic free layer is inversed by injecting a spin-polarized current into the magnetic free layer of a memory element. A current required for writing decreases due to downsizing of a magnetic free layer, and thus, this technique is expected to be an MRAM writing technique.
However, the current density required for spin injection writing of a conventional TMR element is as high as the order of 8×106 A/cm2, and thus, destruction of a tunnel barrier or large-sized peripheral circuits becomes problematic (refer to Yiming Huai et. al., Appl., Phys. Lett. 84 (2004)3118)). Therefore, it is necessary to reduce a write current in order to achieve stable writing without occurrence of destruction of TMR elements. In addition, this is an indispensable technique because reduction of a write current leads to reduction of power consumption when the technique is applied to an MRAM.
In this manner, in the conventional magneto-resistance element, the current density required for spin injection writing is as high as the order of 8×106 A/cm2, and thus, the destruction of a tunnel barrier and large-sized peripheral circuits become problematic.